1. Field of the Invention
The present invention relates to various solid-state imaging devices such as a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor, and more particularly to a solid-state imaging device which is capable of effectively reducing noises contained in an imaging signal, and an imaging apparatus using the same.
Also, the present invention relates to a solid-state imaging device and a camera, and more particularly to a solid-state imaging device in which pixels each having a photodiode in its light receiving surface are arranged in matrix, and an imaging apparatus including the same.
2. Description of the Related Art
In recent years, solid-state imaging devices typified by a CCD image sensor and a CMOS image sensor have been actively developed, and are used in the various camera apparatuses, mobile phones and the like.
For example, in the CCD image sensor, a plurality of pixels each having a photodiode (photoelectric conversion portion) are two-dimensionally disposed on a semiconductor substrate. In addition, a CCD vertical transfer register is provided between each adjacent two pixels. Also, a CCD horizontal transfer register is provided in an output terminal of each of the CCD vertical transfer registers.
In addition, laminated films such as an insulating film, a transfer electrode film, and a light shielding film are formed in order on the semiconductor substrate, and a color filter, a microlens, and the like are formed on the semiconductor substrate through a flattened film or the like.
In such a CCD image sensor, a drive pulse is supplied to the transfer electrode formed on the semiconductor substrate, thereby driving each of the transfer registers. Signal charges generated in the photodiode of the pixel are successively transferred through the CCD vertical transfer register and the CCD horizontal transfer register. Also, the signal charges are then converted either into a voltage signal or into a current signal by the photoelectric conversion portion provided in an output terminal of the CCD horizontal transfer register. Also, the resulting voltage signal or current signal is then outputted in the form of a pixel signal.
On the other hand, in the CMOS image sensor, an imaging region and a peripheral circuit region are provided on the same semiconductor substrate. Here, a plurality of pixels each having a photodiode formed therein are two-dimensionally disposed in the imaging region. Also, the peripheral circuit region is provided outside the imaging region.
In addition, various pixel transistors such as a read transistor (transfer gate), an amplification transistor, a selection transistor, and a reset transistor are provided every pixel in the imaging region. Here, the read transistor reads out the signal charges generated and accumulated in the photodiode to a floating diffusion (FD). The amplification transfer generates the pixel signal corresponding to a potential at the FD. The selection transistor selects the pixel from which the pixel signal is to be outputted. Also, the reset transistor resets the FD. In addition, the signal charges generated and accumulated in each of the photodiodes of the pixels are converted into the pixel signal through the drive for each of the pixel transistors. Also, the resulting pixel signal is outputted through a signal line provided every pixel column.
In addition, a drive control circuit, a signal processing circuit, a power source control circuit, and the like are provided in the peripheral circuit region. Here, the drive control circuit controls an operation for reading out the pixel signal in accordance with the various control pulses supplied to a pixel array portion. The signal processing circuit executes the various signal processing for the pixel signal thus read out. Also, the power source control circuit generates a power source voltage from a driven power source.
In addition, laminated films such as an insulating film, a transfer driving electrode film, a wiring film, and a light shielding film are formed in order on the semiconductor substrate. Also, a color filter, a microlens, and the like are formed on the substrate through a flattened film or the like.
In such a CMOS image sensor, the signal charges accumulated in the photodiode of each of the pixels by driving each of the pixel transistors are converted into the pixel signal every pixel. The resulting pixel signal is outputted every pixel column to be sent to the signal processing circuit in a subsequent stage, and the noise removing processing, the signal processing and the like are executed for the pixel signal in the signal processing circuit. Also, the resulting signal is then outputted from the signal processing circuit.
Now, in the various solid-state imaging devices as has been described above, an area of the photodiode per one pixel is decreased along with the recent multiple pixel promotion. As a result, a quantity of light reaching the photosensitive conversion portion is also reduced, thereby reducing a sensitivity of the photosensitive conversion portion.
For this reason, especially in a low illuminance intensity, an influence of noises exerted on an image quality becomes large, and thus it is necessary to improve an S/N ratio.
Heretofore, it has been known that the noises are suppressed by supplying hydrogen to the photoelectric conversion portion and the transistor region.
FIG. 15 is a cross sectional view showing a pixel structure of a CMOS image sensor according to a related art example.
Firstly, in an upper layer portion of a silicon (Si) substrate 400, a photodiode (PD) 410 and a pixel transistor (Tr) 420 are formed in a region isolated by isolation portions 401. In addition, a lower laminated film 430 including a gate insulating film, a gate electrode film for transistor drive, and the like is disposed on a surface of the silicon substrate 400. Also, a plurality of wiring films 450 are formed on the lower laminated film 430 through various interlayer insulating films 440.
Also, in the related art example shown in FIG. 15, a hydrogen desorbing film 460 containing therein hydrogen is formed above the various interlayer insulating films 440, and a color filter 480 and an on-chip microlens 490 are formed on the hydrogen desorbing film 460 through a protective film 470. This technique, for example, is described in Japanese Patent Laid-Open No. 2002-231915 (Patent Document 1).
In the solid-state imaging device using the CCD element, the CMOS sensor or the like, a light is made incident to the photodiode (photoelectric conversion portion) formed on the surface of the semiconductor substrate. Also, the video signal is obtained from the signal charges generated in the photodiode.
In the CCD element, for example, a plurality of pixels are two-dimensionally arranged in matrix on a light receiving surface, and the photodiode is provided every pixel. Also, the signal charges which are generated and accumulated in each of the photodiodes in a phase of light reception are transferred through a CCD vertical transfer path and a horizontal transfer path to be read out.
In addition, in the CMOS sensor, for example, a plurality of pixels are two-dimensionally arranged in matrix on a light receiving surface similarly to the case of the CCD sensor, and the photodiode is provided every pixel. Also, the signal charges which are generated and accumulated in each of the photodiodes in a phase of light reception are transferred to an impurity diffusion layer called floating diffusion through the drive by a CMOS circuit. Also, the signal charges are then converted into a signal voltage, and the resulting signal voltage is read out.
FIG. 16 is a schematic plan view showing dispositions of photodiodes on a light receiving surface of a solid-state imaging device according to a related art example.
For example, in a photodiode region RPD of a light receiving surface RLR, an n-type charge accumulating layer and a p+-type surface layer overlying the n-type charge accumulating layer are formed every pixel in a p-type well region of a semiconductor substrate. Thus, a photodiode having pn junction is structured.
A light shielding film for shielding incidence of a light is formed in a region, as a light shielding region RSD, other than the photodiode region RPD. For example, in addition to an isolation film for partitioning a light receiving surface into a plurality of regions corresponding to pixels, respectively, a CCD transfer path and the like in the case of a CCD element, and a CMOS circuit and the like in the case of the CMOS sensor are provided in a layer underlying the light shielding film.
In addition, in order to prevent the light made incident to each of the photodiodes from being reflected by a surface of a silicon substrate, an antireflection film is formed so as to cover the photodiodes in the respective photodiode regions RPD.
For example, a silicon nitride film or the like which is lower in refractive index than silicon, and is higher in refractive index than a silicon oxide film as an interlayer insulating film formed so as to overlie the antireflection film is used as a material for the antireflection film.
For the purpose of obtaining a maximum light reflection preventing effect in the solid-state imaging device as has been described above, the antireflection film needs to be formed over the entire surface of the photodiode regions RPD each contributing to the photosensitive conversion.
On the other hand, it is known in the art that a dark current as one of important properties of the solid-state imaging device, for example, can be reduced by terminating dangling-bond of silicon through hydrotreating (sintering).
Here, in the case where the antireflection film is formed over the entire surface of the photodiode regions RPD in the manner as described above, the supply of hydrogen to the silicon region for suppression of the dark current is impeded, so that the dark current increases.
In order to cope with the above problem, Japanese Patent No. 3,070,513 (Patent Document 2) discloses a technique in which a removal region is formed in a silicon nitride film in a lower portion of a CCD transfer gate of a CCD element in order to supply hydrogen.
Japanese Patent Laid-Open No. 2004-165236 (Patent Document 3) discloses a technique in which a removal region is formed a silicon nitride film used as an etching stopper in a CMOS sensor or the like in a light receiving portion in order to reduce the dark current.
Japanese Patent Laid-Open No. 2005-33110 (Patent Document 4) discloses a technique in which a removal region is formed in a silicon nitride film in a photodiode region of a CCD element. Formation of the removal region in the photodiode region promotes processing for terminating the dangling-bond, in the photodiode region, which is thought to greatly contribute to the dark current. As a result, the dark current can be further reduced.
In the case where the removal region in the silicon nitride film is disposed in the photodiode region in the manner as described above, in general, the removal region is disposed in symmetrical shape in the photodiode region. That is to say, the removal regions are formed which have an uniform shape for all the pixels irrespective of positions in the light receiving surface. For example, in the related art example shown in FIG. 16, a pair of stripe-like removal regions RH is formed in left-hand and right-hand end portions of each of the photodiode regions RPD.